The added angle shown above, will increase bending stiffness about 17%. Trouble is that this new angle's flange has the same susceptibility to compression driven buckling as the original. It will decrease compression loads in those angles 17%, which will raise the bending moment before you get to critical load, but I suspect will not be enough. We may need substantially larger resistance to buckling.98933[/ATTACH]
Yes, in a stack like this, it is normal practice to check the crippling stress for each element separately. They do not behave as one homogeneous angle of X number of lamination's in thickness.I built and tested a wing D-cell almost like this. The caps were stacked (laminated) .032" 2024-t3 formed angles.
The laminated angles didn't work as expected and started to buckle in compression between the rivets. I added an additional angle of .125" extrusion. The lesson was that laminations are not the same as a solid bar or a thick angle in compression.
No need to comment at this time but something to think about.A worthwhile improvement but a lot of extra rivets to add.
If the Caps are able to carry the bending load, will the web still wrinkle/collapse?, and what about the stiffeners? If they do not fail/buckle how does the web and spar fail? What might it look like?Again this does not mean that the spar web will fail - it can continue to sustain higher loads once the initial buckling stress has been passed but additional bending load added after buckling will need to be carried by the caps.